This invention relates to matrix addressable display devices, and more particularly to a method and apparatus for testing the emission of the display.
Quality assurance requires the testing of manufactured products to determine if they will function over a given set of parameters. Testing is performed on a random sampling of products from the production lines, or in some industries, on every product which is manufactured.
Optical measurements are currently performed on display devices at the final stages of display testing. Optical measurement is accomplished by turning on all the cathode emitters in a pixel, and visually observing them. This method is extremely subjective, as it relies on the judgement of the individual peering at the screen.
Photon Dynamics of Milipitas, Calif. employs a method in which photons from a full display (i.e., substantially all of the pixels are turned xe2x80x9conxe2x80x9d at the same time) are measured. A completed display device is optically tested by measuring the light emitted from the display.
There are several drawbacks to the above described optical method. For example, the process is very expensive, as it requires sophisticated optics and processing algorithms in order to determine the relative number of functional pixels.
Additionally, the optical systems require closely spaced anodes with respect to the cathode in order for the inspection optics to obtain accurate measurements. Therefore, the optical systems are not practical for testing display baseplates prior to their assembly in a field emission device.
Other methods used to measure current emitted by field emitter devices employ a positively biased electrode. However, these methods also measure the total current emitted by substantially all of the pixels in the completed unit. Therefore, these methods are also limited to measuring the operation of the device as a whole.
There still exists a need for a method to measure the current emitted by individual pixels in the display in order to determine their functionality, as well as the total number of functioning pixels (also known as the xe2x80x9cyieldxe2x80x9d). Additionally, manufacturing realities require that the functionality of the individual pixels is measured in a rapid fashion.
The functionality of individual pixels in an addressable emissive cathode is determined by measuring the emitted current from a single pixel or from a small group of pixels. The current is measured on an anode screen disposed above the cathode emitters, thereby enabling the anode to collect electrons emitted from the cathodes. The collected current is compared to known parameters in order to determine whether the individual pixel site is functional.
The method of the present invention allows for the testing of cathode emitters in a vacuum chamber through the use of probe cards or sockets, and an anode. This format allows for the testing of approximately 100,000 pixels in less than 30 seconds, thereby expanding testing capabilities. Not only does the present technique permit faster testing, but also a less expensive alternative to the functionality tests used for individual pixels.
One advantage of the test method of the present invention is that it enables rapid determination of individual pixel functionality of the cathode emitters used in field emission type displays, or other similarly addressed matrix displays. For example, the present test method is suitable for displays that are actively or passively addressed.
The method of the present invention permits testing of the cathode emitters as a baseplate. Additionally, the use of an anode which luminesces under electron bombardment permits the measurement of emitted photons to determine pixel functionality.
The present invention is employed to sequence through all of the pixels, one or more at a time. Additionally, there is no required spacing for the anode in order to achieve accurate measurement. Further the present invention can be used with current optical methods to enhance the value of those methods.
One aspect of the invention comprises a method of electrically testing pixel functionality which comprises releasably disposing a wafer in a socket. The wafer has at least one baseplate comprised of cathode emitters arranged in pixels. The socket has pads. The socket pads are contacted with test pins, and each of the pixels is addressed individually, thereby causing the cathode emitters to emit electrons in a current. The current is collected from each of the pixels on an anode plate.
Another aspect of the invention comprises an anode card useful for measuring emitted current which comprises: a socket in which to dispose a substrate having cathodes; an anode disposed opposite the socket for collecting emissions from the cathodes, a high vacuum existing between the socket and the anode; and contact pins disposed on the anode for making contact with the substrate.
A further aspect of the invention comprises an apparatus useful for testing emissive cathodes comprising: a transparent collector having phosphors disposed thereon, and a wafer support device for releasably supporting a wafer opposite the transparent collector. The socket has contact pins for contacting the wafer. A high vacuum exists between the transparent collector and the wafer support device.